This is proof that a shih tzu and a lab can breed:
I adopted a lab/shih tzu mix and he is amazing. All the fun of a lab with a little bit less size. I wouldn't trade him for the world.
Sure they can breed, but why would you want too? I'm also going to say that it doesn't matter which one is the female and which one's the male. We already have an over population of dogs that are sitting in shelters waiting for homes. The best thing to do would be to have them spayed and neutered. It's a win, win for all involved...
I am not trying to start a war, don't take it as such, I am just a dog lover and respect each breed as it should be. Small dogs are that small dogs , large breed dogs are just that large dogs why mix them????
We have a six month old shitzu lab mix too! Her mother was a shitzu and her dad was a lab. I think she is quite possibly the best dog we have ever owned! She's small but has all the nature of a lab! It was an accidental breeding and not all that safe but I am very happy I got my peachy girl.